The present invention is directed to heat sinks in general, and more particularly to liquid cooled heat sinks for use in dissipating waste heat generated by electrical or electronic components and assemblies.
Research activities have focused on developing heat sinks to efficiently dissipate heat from highly concentrated heat sources such as microprocessors and computer chips. These heat sources typically have power densities in the range of about 5 to 35 W/cm2 (4 to 31 Btu/ft2s) and relatively small available space for placement of fans, heat exchangers, heat sinks and the like.
Existing heat sinks for microelectronics cooling have generally used air to directly remove heat from the heat source. However, air has a relatively low heat capacity. Such heat sinks are suitable for removing heat from relatively low power heat sources with power density in the range of 5 to 15 W/cm2 (4 to 13 Btu/ft2s). With increase in computing speed the power density of the heat sources has increased to 20 to 35 W/cm2 (18 to 31 Btu/ft2s) requiring more effective heat sinks. Liquid-cooled heat sinks employing high heat capacity fluids like water and water-glycol solutions are more particularly suited to remove heat from high power density heat sources. The cooling liquid used in these heat sinks removes heat from the heat source and is then transferred to a remote location where the heat can be easily dissipated into a flowing air stream with the use of a liquid-to-air heat exchanger. Thus, such heat sinks can be characterized as indirect heat sinks.
A typical liquid-cooled heat sink for microelectronics according to the prior art is shown in FIG. 1, and generally comprises a metal block 10 with drilled passages 12. The passages 12 are connected in a serpentine pattern by means of hairpin tubes 14 to form a continuous passage. The microelectronics device 16 is bonded to one face of the block and liquid coolant flows through the drilled passages 12 and hairpin tubes 14. Block 10 can have one or multiple microelectronics devices bonded to a face of the block. Heat sinks of this type have also used a serpentine tube mounted to one side of a block with the microelectronics device bonded onto the other side of the block. These types of heat sinks, however, have limitations to the density of passages 12 therethrough and must be spaced according to the relatively large bend radii of the hairpin tubes 14.
Therefore, these prior art heat sinks exhibit a relatively low heat transfer capability due to wide spacing of the serpentine flow passages, relatively low heat transfer area and low heat transfer coefficient. The conduction losses in the solid base construction of the heat sink further reduces the available thermal potential for heat transfer between the wall and fluid. Also, such heat sinks tend to be relatively heavy and thus introduce undesirably high mechanical stresses on the electronic devices being cooled and the circuit boards-to which the heat sink is attached. In addition, such heat sinks are limited in their ability to extract heat at low range of heat flux through the microelectronics device.
One aspect of the present invention is a liquid-cooled heat sink for use in combination with a heat exchanger to cool electronic or electrical devices attached to said heat sink comprises a metal block having a plurality of circular passageways therethrough defined by cylindrical walls. An inlet is in fluid communication with one end of the passageways for receiving a cooling liquid, and an outlet is in fluid communication with an opposite end of the passageways for outputting the cooling liquid. At least one tape insert is mounted within at least one of the circular passageway, wherein the tape insert longitudinally bisects the circular passageway and further wherein edges of the tape insert abut cylindrical wall.
Another aspect of the present invention is a method of cooling an electrical or electronic device comprising the steps of providing a liquid cooled heat sink of the type including a block having an inlet in fluid communication with a first end of a plurality of parallel passageways therethrough defined by cylindrical walls wherein each passageway includes a tape insert therein and further having an outlet in fluid communication with an opposite end of the passageways. An electrical or electronic device is affixed to a face of the block with a heat conductive adhesive. A liquid coolant is input into the inlet and then caused to pass through the passageways. The liquid coolant is then expelled from the outlet.